We propose to test the hypothesis that long term culture of primary B lymphocytes accelerates senescence in these cells making them a useful and accessible model to study signal transduction defects in aging lymphocytes. Studies to examine the biology of primary lymphocytes from aged murine donors is severely compromised by the expense of animal aging and by the difficulty of finding disease-free donors whose lymphocytes have not been stimulated by exposure to environmental antigens. An in vitro model that would allow an acceleration of lymphocyte senescence could be a powerful tool, making aging studies more accessible to interested researchers, and reducing the variation in results among workers drawing from significantly different animal colonies. We have found that normal primary B cells expressing a human bcl-2 transgene survive unstimulated for prolonged periods in culture. B cells from these long term cultures are stimulated to proliferate with LPS and anti-CD38 as vigorously as freshly isolated input cells. However, in striking contrast cultured B cells become increasingly refractory to anti-Ig and CD4OL driven proliferation. We hypothesize that deficiencies in Ig and/or especially CD40 stimulatory pathways could be the basis for the hyporesponsive phenotype of aged B cells to thymus dependent antigens and that cultured B cells develop these deficiencies in an accelerated fashion. We propose three experimental aims to validate this new experimental model: (l) To compare proliferation of cultured B cells to aged B cells using 4 polyclonal activators; anti-Ig, CD4OL, CD38, and LPS; (2) To quantitate by flow cytometry the expression of ligand receptors on unactivated cells, and the induction of costimulators and activation molecules on young, aged and cultured B cells after stimulation with selected polyclonal activators; (3) To assess NF-kappa B activation induced by all four activators in cultured and aged B lymphocytes.